In coral reef ecosystems, in the midst of stony corals, algae fronds and schools of fish, microorganisms are essential for the recycling of nutrients: transforming fragments of organic matter into forms of nitrogen and phosphorus, for example, which are useful for photosynthetic organisms.
A study published today in Communications of nature by researchers from San Diego State University (SDSU), the University of Hawaii & # 39; i in Mānoa, the Scripps Institute of Oceanography and others revealed that the bacteria present in the water on dozens of coral reefs changed dramatically during the night , and then returned to the same day of the community as observed the previous morning. In addition, as if these communities were aware of the same program, these changes were synchronized across reefs separated by hundreds of miles.
"Investigations of the day-night rhythms of reef processes are required to comprehensively understand the functional roles of microbial players in these ecosystems," said Linda Wegley Kelly, badistant professor of research at SDSU and co-author and lead author of the study. .
In 2013, an international team of researchers cruised the South Line Islands, a remote chain of equatorial islands south of Hawaii, to measure a series of reef processes. To avoid the dangers of the navigation and diving operations at night, an autonomous sample was designed to collect a sample of water just above the coral reef at midnight. By collecting samples in this way, the researchers measured the changes in water chemistry and the types of microbes present compared to the day at numerous sites. The team also used genomic tools to show how these community changes determine the microbial processes in the reefs that differ day and night.
"Previous studies of marine microbes have shown that different functional groups change their activity throughout the day, but microbial populations remain relatively constant throughout the cycles," said Craig Nelson, badistant professor of oceanography at the School. of Science and Technology of UH Mānoa and co-leading study. "Those who study the reefs know that these ecosystems change significantly from day to night, but this study reveals a previously invisible aspect of that change: a dramatic and predictable change, not only in what the microbes do, but which groups are more abundant" .
The team discovered that a group of microbes called Psychrobacter It seems to be leading the way. Surprisingly, Psychrobacter It can represent 40-70% of the marine microbial community during the day and is a hundred times more abundant than during the night. But what is influencing. Psychrobacter?
"The changes we observe in the composition of microbes during a day-night cycle imply that coral reef habitats manipulate the surrounding sea water, both chemistry and microbiology, depending on the day and night activities of the collective local biota, "said Kelly. "This function can modulate the amount of microbes in the water, promote the cycle of energy through the reef's food web or provide stabilizing effects to the ecosystem."
"This research team is one of the first to observe changes in the microbial communities of coral reefs both day and night," says Dan Thornhill, program director of the Ocean Sciences Division of the National Science Foundation. , who financed the study. "These scientists found striking and striking differences in microorganisms by time of day, and the study also found the important role of nocturnal microbes in nutrient recycling in reefs."
Given the apparent importance of PsychrobacterThe next team seeks to bademble its genome, isolate the bacteria in the culture and further examine the biology of this organism.
The authors' ongoing work shows how the condition of the reefs, that is, healthy or stressed, the dominance of corals or algae, can alter the quantity and types of microbes in the surrounding seawater. This highlights the environmental consequences of altering the benthic habitats of the reefs; where the loss of fundamental calcifying organisms eliminates the processes that affect coastal waters that provide connectivity between land and sea.
Communications of nature (2019). DOI: 10.1038 / s41467-019-09419-z
The bacteria that surround the coral reefs change in synchrony, even at a great distance (2019, April 12)
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